It is known to provide work vehicles, such as industrial articulated loaders, for example, with electro-hydraulic (EH) steering control systems. One advantage of electro-hydraulic systems over pilot controlled systems, e.g. systems that use a joystick to control the flow of pilot fluid to a pilot-controlled steering control valve, is that the metering curve of the EH systems can be easily modified and can even be changed during operation based on input from the operator or machine operating conditions. U.S. Pat. No. 7,283,900 granted Oct. 16, 2009 discloses an EH steering control system wherein a controller unit is used to store a plurality of flow-metering curves representing different steering ratios respectively corresponding to different vehicle speeds, with the controller unit acting in response to steering and vehicle speed signals for sending a representative steering control signal for effecting operation of a steering valve for effecting a desired steering response. Another EH steering control system is disclosed in U.S. Pat. No. 7,200,993 and includes redundant steering pilot valves which operate when primary pilot valves do not operate satisfactorily as determined by sensed pressures.
A disadvantage of EH steering control systems is that they typically add additional failure modes to the machine. These failure modes make it difficult to use the EH steering control systems for “safety critical” functions like steering.
The problem to be solved then is that of providing a steering control system which has the aforementioned advantage of EH steering control systems without requiring failure mode redundancies which add complexities and cost.